The spread behaviors of the underwater oil droplet on smooth brass substrate were studied using high⁃speed microscopic imaging technology. Chemical and physical modifications were made on the surface of the brass sheet to change its surface properties, and the controllable regulation of superoleophilic–superoleophobic wettability gradient of the surface was achieved successfully. The spreading length and contact angle of the oil droplet rising to different modified surfaces were tested. Different from that in air condition, influence of water surrounding the oil droplet must be considered, which is complicated in water. In this work, on the basis of the energy conservation mechanism, quantitative relationship among the eigenvalues for the spreading behaviors of the oil droplet rising to the surfaces, such as droplet dimensionless spreading length, the droplet impact velocity, droplet size, droplet properties, viscosity of the water and surface wettability, were obtained. An optimized spreading dynamic model was constructed to describe the spreading behaviors of underwater oil droplets on surfaces with different wetting properties, to give support for the design of new oil⁃water separation equipment.

Massive electric charges will be generated due to the contact of oils flowing in the non⁃metallic pipeline with the inner wall of the pipeline. Excessive charge gathering discharge will cause spark discharge, which will lead to perforation of the pipe wall and fire, and seriously affect the normal production. Through analysis on the cause of static electricity and influencing factors, it is easy to find that the electrification rate is influenced by the oil flow rate, temperature, water content, pipe material and roughness. The results show that there is a positive correlation between the electrification rate and the oil flow rate, between the electrification rate and the pipe roughness; the rise of oil temperature adversely affects the accumulation of oil static; the electrification rate grows with the moisture content in a certain content range, and decreases with the increase of water content beyond the range; in combination with the existing experiment data, an oil flow⁃induced static model is built.